1. Field of the Invention
The present invention relates to a power or moment regulation device for an adjustable hydraulic pump having a hydraulic servo setting apparatus for providing for a smooth stepless setting of the pump delivery quantity. In the device, the delivery quantity setting is determined in dependence upon the delivery pressure of the hydraulic pump in a delivery pressure line and a control pressure in a control line. The setting apparatus has a spring setting the pump setting member in the direction of maximum delivery quantity and at least one piston acting upon the pump setting member in the direction of delivery quantity reduction. The piston can be acted upon via a hydraulically actuated control valve with the delivery pressure or is connected with a discharge. The actuation of the control valve is effected by means of the control pressure in the control line, whereby a moment valve is provided the closure force of which is determined by a metering spring arrangement which is connected with the pump setting member and is biased in dependence upon the delivery quantity setting. The moment valve connects the control line with the discharge in dependence upon the control pressure in the control line and the biasing of the metering spring arrangement.
2. Description of the Prior Art
Such a regulation device is known from EP 0 149 787. This known regulation device is operable either as a moment regulator or as power regulator, in dependence upon whether or not a delivery flow choke, which may be adjustable, is provided in the delivery pressure line of the hydraulic pump. With such regulation devices there is a direct functional relationship between the stroke volume of the pump and the load-dependent operating pressure upon which the control pressure acting upon the control valve is dependent. For moment regulation there applies the relationship that the product of operating pressure and stroke volume of the pump must be constant. If the speed of rotation of the pump is constant, moment regulation is at the same time power regulation. With power regulators, changes in the speed of rotation of the pump, which affect for example the delivery flow quantity, are additionally detected and regulated. A measure for the stroke volume of the hydraulic pump is the setting of the pump setting member which sets the pump delivery quantity, which is connected via a metering spring arrangement with the moment valve. The shape of the hyperbolic moment or power characteristic is determined solely by the configuration of the characteristic of the metering spring arrangement.
This known power or moment regulation device is very strongly dependent upon the operating delivery quantity taken on the load side from the operating pressure line. Upon an alteration of the operating delivery quantity, the control oil quantity in the control line also changes, so that the pump is displaced along its power hyperbola. A change of the position of the power hyperbola, that is a change of the power setting of the pump, is possible only via the direct adjustment of the biasing of the metering spring arrangement by manual means. This adjustment by hand is very inconvenient and complex. In particular applications, for example in excavator vehicles or the like, it is however necessary to be able to alter the power setting of the pump in dependence upon the kind of work being undertaken or in dependence upon the speed of rotation of the diesel motor driving the pump.